1. Field of the Invention
The present invention relates to a compact sorter for transferring semiconductor wafers or other workpieces between cassettes and/or work stations, and in particular to a modular sorter in which additional modular sections may be added and removed, and in which processing speed of the workpieces may be increased over conventional sorters.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
In order to transfer wafers between a SMIF pod and a processing tool within a wafer fab, a pod is typically loaded either manually or automatedly onto a load port assembly on a front of the tool. The processing tool includes an access port which, in the absence of a pod, is generally covered by a port door. Once the pod is positioned on the load port, mechanisms within the port door unlatch the pod door from the pod shell and the pod door and shell are thereafter separated. A wafer handling robot within the processing tool may thereafter access particular wafers supported in wafer slots in the pod or cassette for transfer between the pod and the processing tool.
One example of a processing tool in a wafer fab is a wafer sorter which is used at various points during the semiconductor fabrication process to perform a number of different functions. One such function of a wafer sorter is to transfer one or more wafers between the various cassettes positioned within the wafer sorter. The wafers can be transferred between the cassettes in the same order or reordered as desired. Another function of a wafer sorter is to map the location of wafers within a cassette, and to detect incorrect positioning of wafers within a cassette.
Wafer alignment and identification may also be carried out in a wafer sorter by a tool referred to as an aligner. Conventional aligners include a chuck for supporting and rotating a wafer and a sensor for identifying a radial runout (i.e., a magnitude and direction by which the workpiece deviates from a centered position on the chuck), and for identifying the position of a notch located along the circumference of the wafer. Aligners generally further include a camera for reading an optical character recognition (OCR) mark that identifies the workpiece. The OCR mark is provided a known distance from the wafer notch, so that once the notch is located, the wafer may be rotated to position the OCR mark under the camera. In a conventional wafer sorter, wafers are transferred one at a time to the chuck of the aligner by a wafer handling robot further provided within the sorter. The chuck then rotates the wafer to allow the radial runout to be determined, the location of the notch to be identified, and the OCR mark to be read. Thereafter, the wafer is reacquired by the robot on center, and returned to one of the cassettes positioned on the sorter.
Typical wafer fabrication recipes utilize two-wide sorters, i.e., sorters including two side-by-side load port assemblies capable of together loading two wafer-carrying cassettes into the sorter. However, occasionally, operations require three-wide sorter units and four-wide sorter units, for example where it is desired to split wafers from one cassette into two or three other cassettes, or visa-versa. Though seldom used, semiconductor manufacturers must provide three-wide and four-wide sorters. While it might be possible to utilize a four-wide sorter in all operations and only utilize that portion of the sorter necessary for a particular operation, four-wide sorters take up valuable floor space in the wafer fab.
A further disadvantage to conventional wafer sorters is the speed with which wafer transfer and aligner operations are carried out. In conventional sorters, the workpiece handling robot must first transfer the workpiece from the cassette to the aligner, the aligner then identifies the radial runout, notch position and OCR mark and then the robot transfers the wafer back to the original or new cassette. The robot sits idle while the aligner performs its operations, and the aligner sits idle while the robot transfers the wafers to and from the aligner. Conventional workpiece sorters therefore have a relatively low throughput, on the order of approximately 200-250 workpieces per hour. As there are several workpiece sorters within a fab, this low throughput can become significant.
It is known to provide dual armed robots to increase throughput. One such dual armed robot is disclosed in U.S. Pat. No. 5,789,890 to Genov et al., entitled xe2x80x9cROBOT HAVING MULTIPLE DEGREES OF FREEDOMxe2x80x9d. As disclosed therein, such robots typically include multiple arms offset from each other so as to be able to obtain a first workpiece from the cassette, spin around, and then acquire a second workpiece. Such robots take up a significant amount of space within the sorter, where space is at a premium owing to the expense of maintaining the ultraclean minienvironment. Moreover, typical dual armed robots are expensive, and require more complicated controls.
It is therefore an advantage of the present invention to provide a modular sorter in which the number of load port assemblies affixed to the sorter may be increased or decreased.
It is another advantage of the present invention to reduce equipment costs and to promote more efficient usage of equipment through the use of modular sections.
It is a further advantage of the present invention to increase throughput by reducing idle time of the aligner and idle time of the workpiece transfer robot.
It is a still further advantage of the present invention to provide a centralized control unit which may be easily accessed for repair, upgrade or replacement of controller components.
It is another advantage of the present invention to provide a centralized control unit which allows quick and easy addition or subtraction of modular sections to the modular sorter.
It is a further advantage of the present invention to provide a modular sorter of compact size.
These and other advantages are provided by the present invention which in general relates to a modular sorter in which modular sections may be easily added and removed to add and remove load port assemblies as required by a particular wafer manufacturing facility. In one embodiment, a modular sorter according to the present invention includes a two-wide modular section defining a minienvironment for the sorter, a wafer handling robot, a pair of aligners and a centralized controller. The modular section of this embodiment includes a pair of side-by-side load port assemblies for receiving a container or open cassette and presenting the cassette to the sorter minienvironment for processing of the wafers therein.
The two-wide modular section sorter may be easily modified to include additional modular sections with additional load port assemblies. In particular, the present invention includes a removable end panel affixed for example by removable bolts to the end of the two-wide modular section. When it is desired to add additional modular sections to the sorter, the end panel is removed and replaced by a connector frame. An additional modular section, having either one or two load port assemblies, may then be attached to the connector frame.
All of the power and control components for the modular sections are preferably located in the centralized controller. Upon attachment of the additional modular section, the power and signal connections for the additional section are plugged into the controller. The controller may then be configured operate as a three-wide sorter or a four-wide sorter through simple commands entered via the controller graphical interface. It is contemplated that the controller alternatively recognize the additional modular sections automatically, and configure the system to operate accordingly.